This invention relates to a printed circuit board and more particularly to such a board comprising a material through which optical energy can be transmitted.
Printed circuit boards are commonly used as a support for a variety of electrical components as is well known. It is also well known that laser diodes are amongst the components secured to a printed circuit board.
Laser diodes are constructed from a plurality of suitable layers on a substrate. The layers form a quantum well which defines an emitting facet for light energy. The quantum well is sandwiched between waveguiding layers which, in turn, are sandwiched between cladding layers as is well understood.
Printed circuit boards which include lasers also typically require sensors which are responsive to laser emissions. Such sensors have to be placed in an optical path of the laser output. Consequently, constraints are placed on the position of the sensors and applications for photosensitive circuits, thus, are limited.
In accordance with the principles of this invention, the circuit board itself is constructed of a material which transmits light energy and thus functions as a waveguide. Further, reflective coatings are added to the opposite faces of the circuit board to enhance the waveguide properties. Light directed at the edge of the circuit board may be sensed by a sensor located anywhere on the face of the board at a window opened in the coating there. Constraints on the placement of sensors are relaxed.